This invention relates to a system for guiding missiles to a target. More particularly, the invention relates to a missile guidance system where the missile is guided to its target by a polarization-agile beam.
Beamrider guidance is used to direct missiles to their targets in several military systems. Basically, a beamrider guidance system uses one or more beams directed into space such that the axis of the beam is directed toward the intended target of a missile. The beam, which may be either millimeter or light, contains a code such that a missile with an appropriate receiver can receive the beam and determine its relative position within the beam. If the missile deviates from the beam axis, aerodynamic surfaces coupled to the receiver are moved to direct the missile back to the axis.
There are various known techniques used in beam guidance. One is to have a single non-nutating beam directed toward the rear of the missile as the missile flies toward a target. Missile movements that cause it to deviate from the axis of the beam are detected by a decrease in amplitude of beam radiation received by the missile. The receiving device can be structured so as to cause the missile to return to the center of the beam axis. U.S. Pat. No. 3,782,667 entitled "Beamrider Missile Guidance Method" issued to Miller et al discloses such a system.
Another known guidance method is a nutating beam that forms conical scanning. The nutation is synchronized with operations in the missile receiver. The receipt of the radiation on the receiver can thus cause the missile to return to the center line axis around which the beam nutates. The Miller et al patent also discloses this method.
A third known method uses four non-nutating parallel beams, with the intended missile path being the axis formed by all four of the beams. Each beam is distinguishable from the others by means of having a unique frequency or some other distinguishing characteristic. The receiver on the rear of the missile operates such as to let the missile know which beam or beams it is flying in when it veers from the center line axis of the corridor that is formed by the four beams. This information allows the missile to adjust its line of flight to return to the axis. U.S. Pat. No. 4,501,399, for "Hybrid Monopulse/Sequential Lobing Beamrider Guidance" issued to Loomis discloses this method.
A primary consideration for all beamrider systems is the nature of the beam being used. Laser beams have a limitation of not being able to penetrate dust or heavy smoke and thus are not well adapted to ground-to-ground battlefield conditions where a lot of dust or smoke is likely to be generated. Likewise, simple millimeter wave beams may be susceptible to electronic countermeasures which would diminish their effectiveness. Thus, it is desirable to use beams that can penetrate dust and smoke, and to be resistant to electronic countermeasures. The present invention exhibits these desirable characteristics.